The present invention relates to a method for extracting morphological characteristics of biological materials, in particular fingerprints and especially internal or external fingerprints, using signals delivered by optical coherence tomography acquiring devices, especially for biometry.
The optical coherence tomography (OCT) imaging technique is a contactless optical imaging technique that is currently commonly used in the medical sector. It is starting to be used in mass-market applications and especially in biometric applications. At the present time, the problems specific to this type of application are different and intimately related to the study of the properties of surfaces defined from raw three-dimensional data.
By design, an SW-OCT imaging device is an interferential device based on a (Michelson or Mach-Zender) interferometer and a tunable source. Each measurement consists in recording the interferometric signal as a function of the frequency of the source. Complex signals (intensity and phase) are therefore recorded raw in the spectral domain.
These signals are usually represented in the spectral domain (or temporal domain since position may be equated to a time of flight of the light) after Fourier transform of the recorded signal. The complex signal thus obtained is called an A-scan.
For a static object (i.e. an immobile object not subjected to temporal deformation), the spatial phase varies linearly with distance along the z-axis in the vicinity of each achromatic (or reflective) scattering centre.
When the object possesses dynamic properties (deformation and/or movement), any variation in the spatial phase at different measuring times is associated with a Doppler shift.
The spectral phase associated with a scattering centre varies linearly with the frequency υ of the source. The slope of the phase in the spectral domain, which slope is defined by dϕm/dυ, is proportional to the spatial position of the scattering centre (or to the time of flight taken by the light to reach the scattering centre).